Interstellar Neutral Gas Species And Their Pickup Ions Inside The Heliospheric Termination Shock. Ionization Rates For H, O, Ne, And He

Abstract

Solar ionizing factors are responsible for modulation of interstellar neutral gas and its derivative populations inside the heliosphere. We provide an overview of the current state of knowledge about them for heliospheric particles inside the termination shock. We discuss charge exchange with solar wind particles, photoionization, and electron impact ionization for hydrogen, oxygen, neon, and helium from 1985 to 2018 both in the ecliptic plane and in the polar regions. We discuss ionization rates as a function of time, distance to the Sun, and latitude. We compare the total ionization rates among the species within a consistent and homogeneous system of calculation of the ionization rates. The highest total ionization rates at 1 au in the ecliptic plane are for hydrogen and oxygen, and the lowest are for helium. In the polar regions, the strongest ionization losses are for oxygen, regardless of the solar activity. Photoionization is the dominant ionization reaction for helium and neon, and a reaction of high significance for oxygen. Charge exchange with solar wind particles is the dominant ionization reaction for hydrogen and the second important ionization reaction for oxygen. Electron impact ionization is an important ionization reaction for Ne and He, with the contribution to the total ionization rates stronger within 1 au and smaller outside. The total ionization rates for He and Ne vary in time with the solar activity, whereas the total ionization rates for H and O follow the cyclic solar wind variations out of the ecliptic plane and aperiodic variations in the ecliptic plane.

arXiv comment12 pages, 8 figures, 2 tables, published in The Astrophysical Journal

References in corpus (13)

• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• The Solar Wind Around Pluto (SWAP) Instrument Aboard New Horizons
• Heliolatitude and time variations of solar wind structure from in situ measurements and interplanetary scintillation observations
• Survival probability and energy modification of hydrogen Energetic Neutral Atoms on their way from the termination shock to Earth orbit
• Solar parameters for modeling interplanetary background
• Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX
• The Solar Wind Energy Flux
• Reconstruction of Helio-latitudinal Structure of the Solar Wind Proton Speed and Density
• Is the solar spectrum latitude dependent? An investigation with SST/TRIPPEL
• Evolution of the Solar Lyman-Alpha line profile during the solar cycle
• Ionization rates in the heliosheath and in astrosheaths
• Evolution of the solar Ly-$\alpha$ line profile during the solar cycle. II. How accurate is the present radiation pressure paradigm for interstellar neutral H in the heliosphere?
• Solar cycle variation of interstellar neutral He, Ne, O density and pick-up ions along the Earth's orbit

Cited by in corpus (16)

• Sun-Heliosphere Observation-based Ionization Rates Model
• Interstellar neutral helium in the heliosphere from IBEX observations. VI. The He${}^{+}$ density and the ionization state in the Very Local Interstellar Matter
• Turbulence in the outer heliosphere
• Very Local Interstellar Medium Revealed by Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX
• Interstellar Neutral Gas Species And Their Pickup Ions Inside The Heliospheric Termination Shock. The Large-scale Structures
• A new 3D solar wind speed and density model based on interplanetary scintillation
• Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions Beyond the Heliopause
• Signature of a heliotail organized by the solar magnetic field and the role of non-ideal processes in modeled IBEX ENA maps: a comparison of the BU and Moscow MHD models
• The Confinement of the Heliosheath Plasma by the Solar Magnetic Field as Revealed by Energetic Neutral Atom Simulations
• Angular Scattering in Charge Exchange: Issues and Implications for Secondary Interstellar Hydrogen
• Science Opportunities from Observations of the Interstellar Neutral Gas with Adjustable Boresight Direction
• On general correlation between 3D solar wind speed and density model and solar proxies
• Interstellar Neutral Hydrogen in the Heliosphere: New Horizons Observations in the Context of Models
• Heliospheric structure as revealed by the 3 -- 88 keV H ENA spectra
• Energetic neutral atoms from the heliosheath as an additional population of neutral hydrogen in the inner heliosphere
• Turbulence in the Local Interstellar Medium and the IBEX Ribbon